Wednesday, September 19, 2018

PRO/AH/EDR> Tick-borne encephalitis - Switzerland (05): comment

TICK-BORNE ENCEPHALITIS - SWITZERLAND (05): COMMENT
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Date: Mon 17 Sep 2018
From: Ivo Foppa <ivo.foppa@gmail.com> [edited]


I commented on TBE [tick-borne encephalitis] incidence in Switzerland
a little less than a year ago. In fact, last year (2017), had been the
year with the highest number of reported TBE cases (269) thus far,
exceeding the previous record year, 2006, by around 25 cases. Current
year's [2018] case numbers already exceed last year's record numbers
by far already (325), even though many more cases, maybe around 100,
are expected to occur until the end of this transmission season.

The current year-to-year upward cascading pattern is reminiscent of
the years 2003 to 2006, after which the annual case numbers were
consistently well above 100. I expect a similar upward reset of the
annual baseline after the current series of seasonal increases.
Whether some of that increase may be due to a change in reporting
practices will have to be determined. However, the remarkable
consistency of the total case/hospitalized cases ratio (hospitalized
cases were reported only until 2001) suggests that at least part of
this increase is real.

Persistence and spread of tick-borne encephalitis in
Central/Western/Northern Europe, given the current paradigm of
enzootic perpetuation, is implausible (1). So why has TBE incidence
been increasing substantially over the past 3 or more decades? The
most consistently offered explanation is "climate change" (2), but a
linear mechanism is unlikely to linearly affect the complex system of
TBE perpetuation.

Anthropogenic ecological changes, too, have been implicated in
increasing TBE incidence (3). Unfortunately, Federal funding agencies
have not been keen in supporting research aiming at exploring the
underlying root causes -- at least not when I last tried 8 years ago.

References
----------
1. Foppa IM. The basic reproductive number of tick-borne encephalitis
virus. An empirical approach. J Math Biol. 2005; 51(6): 616-28;
<https://link.springer.com/article/10.1007%2Fs00285-005-0337-3>.
2. Mansfield KL, Johnson N, Phipps LP, et al. Tick-borne encephalitis
virus - a review of an emerging zoonosis. J Gen Virol. 2009; 90(Pt 8):
1781-94. doi: 10.1099/vir.0.011437-0;
<http://jgv.microbiologyresearch.org/content/journal/jgv/10.1099/vir.0.011437-0#tab2>.
3. Randolph SE, 2001. The shifting landscape of tick-borne zoonoses:
tick-borne encephalitis and Lyme borreliosis in Europe. Philos Trans R
Soc Lond B Biol Sci. 2001; 356(1411): 1045-56;
<http://rstb.royalsocietypublishing.org/content/356/1411/1045.long>.

--
Ivo M Foppa
Battelle/CDC/Emory School of Public Health
<ivo.foppa@gmail.com>

[The number of tick-borne encephalitis (TBE) cases in Switzerland has
increased from 230 on 24 Jul 2018, to 272 on 13 Aug 2018, to 325 one
month later, as listed above. As noted earlier, the virus is endemic
(and expanding) in certain areas of the country, as well as in some
areas of Germany and Austria.

In a previous comment last year (2017) concerning TBE in Switzerland,
Dr Ivo M Foppa indicated that the incidence of TBE in Switzerland has
increased distinctly since 2000, roughly about 50 percent. The reason
for the increase of TBE incidence in Central/Western/Northern Europe
is unknown, as Dr Foppa notes above. He is thanked for his comments.

The WHO has stated that "Approximately 10 000-12 000 clinical cases of
tick-borne encephalitis are reported each year, but this figure is
believed to be significantly lower than the actual total. Immunization
offers the most effective protection. Currently, there are 4 widely
used vaccines of assured quality: FSME-Immun and Encepur, manufactured
in Austria and Germany, respectively, and based on European strains of
the virus; and TBE-Moscow and EnceVir, manufactured in the Russian
Federation and based on Far-Eastern strains. The 4 vaccines are
considered to be safe and efficacious."
(<http://www.who.int/immunization/topics/tick_encephalitis/en/>).

TBE is a viral infection caused by one of 3 tick-borne encephalitis
virus (TBEV) subtypes belonging to the Flaviviridae family: Central
European, Siberian and Far Eastern (formerly known as Russian
spring-summer encephalitis). It is transmitted to humans through the
bite of infected _Ixodes_ ticks. - Mod.TY

HealthMap/ProMED-mail map of Switzerland:
<http://healthmap.org/promed/p/105>]

[See Also:
Tick-borne encephalitis - Switzerland (04)
http://promedmail.org/post/20180915.6031089
Tick-borne
encephalitis - Switzerland (03)
http://promedmail.org/post/20180816.5969701
Tick-borne
encephalitis - Switzerland (02): vaccine recommendation
http://promedmail.org/post/20180725.5926981
Tick-borne
encephalitis - Switzerland
http://promedmail.org/post/20180711.5898522
2017
----
Tick-borne encephalitis - Switzerland (04)
http://promedmail.org/post/20171120.5453967
Tick-borne
encephalitis - Switzerland (03): comment
http://promedmail.org/post/20171017.5387144
Tick-borne
encephalitis - Switzerland (02): comment
http://promedmail.org/post/20171013.5379703
Tick-borne
encephalitis - Switzerland
http://promedmail.org/post/20171010.5371714]
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